NOUN (3)

1. (facetious) a serving of an alcoholic beverage;

2. a serving (of wine) poured out in honor of a deity;

3. the act of pouring a liquid offering (especially wine) as a religious ceremony;

The Collaborative International Dictionary of English v.0.48:

Libation \Li*ba"tion\ (l[-i]*b[=a]"sh[u^]n), n. [L. libatio, fr.
   libare to take a little from anything, to taste, to pour out
   as an offering: cf. F. libation.]
   The act of pouring a liquid or liquor, usually wine, either
   on the ground or on a victim in sacrifice, in honor of some
   deity; also, the wine or liquid thus poured out. --Dryden.
   [1913 Webster]

         A heathen sacrifice or libation to the earth. --Bacon.
   [1913 Webster]

WordNet (r) 3.0 (2006):

libation
    n 1: (facetious) a serving of an alcoholic beverage
    2: a serving (of wine) poured out in honor of a deity
    3: the act of pouring a liquid offering (especially wine) as a
       religious ceremony

Moby Thesaurus II by Grady Ward, 1.0:

61 Moby Thesaurus words for "libation":
   beverage, bumper, burnt offering, collection, draft, dram, drench,
   drink, drink offering, drop, ex voto offering, gargle, gulp,
   guzzle, heave offering, hecatomb, holocaust, human sacrifice,
   immolation, incense, infanticide, jigger, jolt, lap, mactation,
   nip, oblation, offering, offertory, peace offering, peg,
   piacular offering, portion, potation, potion, pull, quaff, round,
   round of drinks, sacramental offering, sacrifice, scapegoat,
   self-immolation, self-sacrifice, shot, sip, slurp, snifter, snort,
   spot, suck, sup, suttee, sutteeism, swig, swill, thank offering,
   tot, votive offering, wet, whole offering